I think a state would probably work. For example, you cast a fire spell on an empty tile and it adds a burn state.
And anyone that walks into it might automatically gain the burn state.
You could then have the sprite reflect the state that's applied. Not sure what happens if there's multiple states but probably something that devs would figure out for their game.
I also really like this idea of being able to dynamically change the terrain state of a tile. In terms of multiple states, I think if there's some way to designate a "priority" number of each state, then the highest priority state could always takes over. Or even better, if you allow some kind of note-syntax or similar that allows someone to assign an "end result" state based on combinations of other states ("fire" + "ice" = "water"). It'd be nice if there was some built in support for making those a + b = c or a + c + d = w kinds of assignments.
